The proposed plan consists of three main projects. The first concerns the human X chromosome and consists of two parts. One is aimed at a deeper understanding of the structure and behavior of this chromosome by means of a very thorough cytological investigation of abnormal X chromosomes. The main source for these will be an ongoing survey of women with primary amenorrhea conducted in the Department of Gynecology and Obstetrics. A focus of interest in this work is the presumed inactivation center located in the proximal region of Xq. The second part of the X chromosome work will be an extensive statistical study of the XO syndrome and related conditions based mostly on a much more thorough evaluation of published cases than has been done before. This will have direct bearing on some aspects of the above mentioned cytological work. The second project covers various problems concerning chromosomes in general such as the behavior of inactivated centromeres in dicentric or even monocentric chromosomes. Another topic is the relation of quinacrine banding and base ratios. This will be investigated by means of autoradiographic grain counts after incorporation into DNA of one or the other of tritiated guanine or tritiated thymidine. Certain methodological problems seem to have been overcome so that clean results may be expected. The third project concerns cancer. One part is aimed ultimately at finding cancer drugs that cause maximal chromosome breakage in malignant cells but minimal harm in normal ones. The other part is an extensive study of mitotic anomalies in cancers of the female genital tract. These will be correlated with various clinical parameters. One purpose of this work is to evaluate the practical potential of the use of mitotic anomalies as a tool in cancer diagnosis as compared with the usual histological methods.